1. Field of the Invention
This invention relates to a light-receiving member sensitive to electromagnetic waves such as light in a broad sense, including ultra-violet rays, visible radiation, infra-red rays, X-rays, .alpha.-rays, etc., and more particularly to a light-receiving member suitable for applications of coherent light such as laser beam, etc.
2. Decription of the Prior Art
A well known method for recording digital image information as an image comprises optically scanning a light-receiving member with a laser beam modulated according to digital image information, thereby forming an electrostatic latent image, then developing the image, and, if necessary, conducting transfer, fixation, etc. of the developed image, thereby recording the image. Among them, a method for forming an image by electrophotography generally records an image, using such a laser as a small and cheap He-Ne laser or semi-conductor laser usually having an emission wavelength of 650-820 nm. As a light-receiving member for electrophotography suitable for applications of a semi-conductor laser, the light-receiving member comprising an amorphous material containing silicon atoms (hereinafter written briefly as "A-Si") as disclosed, for example, in Japanese Laid-open Patent Application No. 86341/1979 or Japanese Laid-open Patent Application No. 83746/1981 is attracting attention for its high Vickers hardness and non-polluting properties in social aspect in addition to the advantage of being by for superior in matching in its photosensitive range as compared with other kinds of light-receiving member.
However, when the photo-sensitive layer is made up of a single A-Si layer, it is necessary that hydrogen atoms or halogen atoms, or boron atoms in addition to thereto are structurally contained in the layer in controlled amounts within specific ranges to obtain a dark resistance of 10.sup.12 .OMEGA..cm or higher required for the electrophotography while maintaining a high photosensitivity. Thus, there is considerable restrictions to the design allowance of light-receiving member such as the necessity for strict control of layer formation, etc.
It has been already proposed to enlarge the design allowance, that is, to effectively utilize the high photosensitivity even if the dark resistance in somewhat low. For example, light-receiving members having an improved apparent dark resistance have been proposed by making up the light-receiving layer of two or more laminated layers having different photoconductive characteristics, thereby forming a vacant layer in the light-receiving layer, as disclosed in Japanese Laid-open Patent Application Nos. 121743/1979, 4053/1982 and 4172/1982, or by providing a light-receiving layer between the substrate and the photo-sensitive layer and/or by providing a barrier layer on the upper surface of the photo-sensitive layer, thereby making the light-receiving member of multi-layer structure, as disclosed in Japanese Laid-open Patent Application Nos. 52178/1982, 52179/1982, 52180/1982, 58159/1982, 58160/1982 and 58161/1982.
According to such proposals, the A-Si type light-receiving members have been drastically advanced in tolerance in designing of commercialization thereof as well as in easiness in management of the production and productivity, and the speed of developement toward commercialization is now further accelerated.
When laser recording is carried out with such a light-receiving member having the light-receiving layer of multi-layer structure, there is a possibility of occurence of interferences of reflected lights from the free surface on the laser beam irradiation side of the light-receiving layer and the layer interfaces between the individual layers making up the light-receiving layer and between the substrate and the light-receiving layer (hereinafter "interface" is used to mean comprehensively both the free surface and the layer interface) because the individual layers are not uniform in thickness and the laser beam is an coherent monochromatic light.
The interference phenomenon appears on the formed visibible image as the so called interference fringe pattern, and deteriorates the image. Particularly in the case of forming a halftone image with high gradation, the image becomes considerably poor. Moreover, as the wavelength region of the applied semi-conductor laser beam is shifted to a longer wavelength, the absorption of the laser beam in the photo-sensitive layer is reduced, and thus the interference phenomenon becomes more pronounced. This point is described in detail, refering to the drawings.
FIG. 1 shows a light I.sub.0 incident upon a certain layer making up the light-receiving layer of a light-receiving member, a reflected light R.sub.1 from the upper interface 102 and a reflected light R.sub.2 from the lower interface 101.
Now, an average layer thickness of the layer is defined as d, a refractive index as n, and a light wavelength as .lambda., and when the layer thickness of a certain layer is ununiform gently within a layer thickness difference of .lambda./2n or more, the light absorption quantity and light transmission quantity change, depending on whether the reflected lights R.sub.1 and R.sub.2 conform the condition of 2nd=m.lambda.(m: an integer, where the reflected lights are strengthened with each other) or the condition of 2nd=(m+1/2).lambda.(m: an integer, where the reflected lights are weakened with each other).
In the light-receiving member of multi-layer structure, the interference effect shown in FIG. 1 occurs in each layer, and a synergistically adverse effect due to the individual interferences occurs, as shown in FIG. 2. Thus, the interference fringes corresponding to the interference fringe pattern appear on a visible image transferred and fixed on a transfer member, deteriorating the image.
To overcome the disadvantage, various methods have been proposed, for example, a method for forming a light scattering surface by diamond-cutting the surface of a substrate thereby providing unevenness of .+-.500 .ANG. to .+-.10,000 .ANG. (Japanese Laid-open Patent Application No. 162975/1983), a method for providing a light absorption layer by subjecting the aluminum substrate surface to black Alumite treatment or by dispersing carbon, coloring pigment or dye into the resin (Japanese Laid-open Patent Application No. 165845/1982), a method for providing a light scattering or reflection-preventive layer on the surface of substrate by subjecting the aluminum substrate surface to satin-like Alumite treatment or by providng a sandy fine uneveness by sand blast (as disclosed in Japanese Laid-open Patent Application No. 16554/1982), and the like.
However, the interference fringe pattern appearing on the image cannot be completely eliminated according to these conventional methods. That is, the first method can indeed prevent the occurrence of the interference fringe pattern by virture of the effect of light scattering, because a large number of projections and recesses within a specific range of sizes are provided on the substrate surface, but the regularly reflected light components still exist in the light scattering and thus there remains the interference fringe pattern due to said regularly reflected light. In addition, the irradiated sports are enlarged due to the light scattering effect on the substrate surface, resulting in lowering of substantial resolution.
The electrolytic oxidation of the aluminum substrate into black according to the second method cannot attain complete absorption, and thus the reflected light still remains on the substrate surface. In the case of providing the coloring pigment-despersed resin layer, the resin layer is deaerated when the A-Si photo-sensitive layer is formed, resulting in considerable lowering of the quality of the formed photo-sensitive layer, and also the resin layer is damaged by the plasma when the A-Si based photo-sensitive layer is formed, resulting in lowering of the proper absorption function and deterioration of the surface state, giving an adverse effect on the successive formation of A-Si based photo-sensitive layer .
In the third method for irregularly roughering the substrate surface, as shown in FIG. 3, for example, the incident light I.sub.0 is partly reflected on the surface of light-receiving layer 302 to form reflected light R.sub.1, while the remaining incident light advances into the light-receiving layer 302 to form transmitted light I.sub.1. The transmitted light I.sub.1 is partially scattered on the surface of substrate 302 to partially form diffused lights K.sub.1, K.sub.2, K.sub.3 . . . as a result of light scattering, while the remaining transmitted light is regularly reflected to form reflected R.sub.2, a part of which is emitted to the outside as outgoing light R.sub.3. Thus, the outgoing light R.sub.3 which is a component interferable with the reflected light R.sub.1, remains, and thus the interference fringe pattern cannot be completely eliminated yet.
When the surface diffusibility of substrate 301 is increased to prevent multiple reflection within the light-receiving layer to prevent the interference, the light is diffused within the light-receiving layer, causing halation and lowering the resolution.
Particularly in the light-receiving member of multi-layer structure, as shown in FIG. 4, the reflected light R.sub.2 on the first layer 402, the reflected light R.sub.1 on the second layer, and the regularly reflected light R.sub.3 on the surface of substrate 401 interfere with one another to form interference fringe patterns according to the thickness of each layer in the light-receiving member, even if the surface of substrate 401 is irregularly roughened. Thus, in the light-receiving member of multi-layer structure, the interference fringes cannot be completely prevented by irregular roughening of the surface of substrate 401.
In the case of irregular roughening of the substrate surface by sand blasting, etc., the roughness much fluctuates between lots, and even one and same low cannot have an even roughness, giving an inconvenience to the production control. In addition, there are many chances to form relatively large projections at random, which cause a local breakdown in the light-receiving layer.
In the case of mere regular roughening of the surface of substrate 501, as shown in FIG. 5, the light-receiving layer 502 is formed along the uneven shape on the surface of substrate 501 and thus the projections and recesses of the surface of substrate 501 will be in parallel with the projections and recesses of the surface of light-receiving layer 502.
Thus, 2nd.sub.1 =m.lambda. or 2nd.sub.1 =(m+1/2).lambda. is valid for the incident light at these surfaces to form bright or dark fringes, respectively. Throughout the entire light-receiving layer, there is such an unevenness in the layer thickness that a maximum difference between the individual layer thicknesses of light-receiving layer, d.sub.1, d.sub.2, d.sub.3 and d.sub.4, is more than .lambda./2n , and thus bright and dark fringe patterns appear. Thus, occurrence of interference fringe patterns cannot be completely prevented merely by roughening the surface of substrate 501.
In the case of forming a light-receiving layer of multi-layer structure on the regularly roughened substrate surface, interferences of reflected lights at the interfaces between the individual layers intract together with the interference between the regularly reflected light on the substrate surface and the reflected light on the light-receiving layer surface, as in FIG. 3, referring to the light-receiving member of single layer structure. Thus, the interference fringe patterns as occurred will be more complicated than that is the light-receiving member of single layer structure.